The Andalusian toothcarp, Aphanius baeticus, is a critically endangered cyprinodontid species, with only nine known extant populations. Although not yet studied in the field, the distri- bution and abundance of Andalusian toothcarp are thought to be strongly influenced by inter- specific interactions. We analysed the abundance and microhabitat use of Andalusian toothcarp in two water courses, one in which several other fish species occurred (sympatric site) and one hy- persaline stream in which toothcarp was the only species present (allopatric site). Fish were sam- pled using plastic minnow traps and results were analysed separately for three size categories. Toothcarps were clearly more abundant in the allopatric population than in the sympatric one, though the difference was less apparent in the smallest size category. In coexistence with other species, toothcarp occupied shallower microhab- itats, but in both sites in the absence of shelter fish selected deeper positions than in its absence. While in the sympatric site sheltered microhabitat were used predominately by small individu- als, in the allopatric ones they were used by larger ones. Observed patterns strongly suggest that predation is the main mechanism involved in the differences in abundance and microhabitat use between sites. Our results confirm that the pres- ence or absence of coexisting species is an important habitat feature for Andalusian tooth- carp populations.

Peer reviewed